Proof-of-concept: real-time image decompression
![Wuerfel_21](https://forums.parallax.com/uploads/userpics/693/n8QPDN86LL3XG.png)
Ever wanted to display (semi-)arbitrary 8bpp pictures on a P1 but ran into the memory limit? Well, yearn no more, because I figured out a way. Still need to implement all features, optimize, clean up, document, etc, but you can have some demoboard-compatible (read: TV out on pins 12,13,14, 5 MHz XTAL) binaries in the mean time. I scoured the internet for some example pictures that'd compress well enough. I'll figure out where/who I got them from later(tm). I can tell you that reimu.binary was drawn by my humble self.
Comments
Is this RLE compression or something fancier?
-Phil
It's actually less fancy, it's basically dynamic bit-depth for different parts of the image - where there are only 4 colors used, a 2bpp+palette format can be used. The palettes are kindof run-length encoded.
So it's run length encoding plus some form of variable length encoding?
Uh kindof I guess. It works like this:
There are 3 decompression cogs that handle lines in an interleaved fashion, like a normal graphics driver would (infact, this is mostly just VJET with the rendering code swapped out).
Each cog has it's own command buffer and data buffer that contain data pertinent to all lines that cog handles. To decompress a line, it reads command bytes from the command buffer until it reaches the end-of-line marker. These commands cause some amount of longs to be read from the data buffer and converted into pixels in some way.
The command bytes encode like this:
The 2bpp pixels are encoded in the JETEngine style delta format, instead of the more usual way.
I just improved the compression ratio quite considerably by turning the previously unused
%iiiiii10
command into an RLE command (that takes its color from the command buffer to keep the data buffer aligned). It can now handle quite a bit more complex images.I'll get everything ready to post the code now.
In the mean time, have some nice screen photos (I could post video capture stills, but those don't look as cool, so I won't)
Here we go - have fun with it.
It is used like this:
ntsc_scronch.pal
or the image attached to this post). Keep in mind that the pixels will be wider than they are tall, about 8/7 ratio.ruby pixcrush.rb my_image.png my_image.dat
demo.spin
in Propeller Tool and change the referenced dat file (you can't miss it). If you want, you can also change the TV pins, enable SVideo or PAL60, etc.And here's where I, uh, borrowed the example images from:
Nice work Wuerfel_21 😁
I just realized that there is no reason this format wouldn't scale to, say, displaying 1080p images on P2. Someone with a P2 should give that a shot.